1. Field of the Invention
The present invention relates to monolithic integrated circuit band gap voltage regulators.
2. Description of the Prior Art
There are many electrical circuit applications in which a stable, constant voltage reference is required. In particular, voltage reference circuits which are capable of fabrication as integrated circuits are particularly advantageous. Examples of prior art voltage reference circuits are shown in U.S. Pat. No. 3,648,153 by Graf; U.S. Pat. No. 4,064,448 by Eatock; and U.S. Pat. No. 4,088,941 by Weatly, Jr.
One type of constant voltage reference circuit which is particularly useful in monolithic integrated circuits is called a band gap voltage regulator, which provides a regulator output voltage which is stable, essentially temperature independent, and approximately equal to the band gap voltage of silicon. One band gap voltage regulator of this type, and other pertinent semiconductor information, is described in the book Integrated Circuit Engineering by Glaser, Subak and Sharpe and published by the Addison-Wesley Publishing Company (1977). The band gap voltage reference described by Glaser, Subak and Sharpe at pages 513-517 uses a pair of identical transistors and a pair of resistors to form a logarithmic current source. A third transistor and resistor are connected to the logarithmic current source to provide an output voltage which is a function of the base emitter voltage (V.sub.BE) of the third transistor and the current flow through the third resistor. By proper selection of the values of the three resistors, the output voltage is temperature compensated and is essentially equal to the band gap voltage. The output voltage of the band gap regulator and the conditions for temperature independence both depend upon the value of V.sub.BE of the third transistor.
Prior to the filing of the present patent application, a search of prior art was performed, and the following patents were identified:
______________________________________ Doucette et al. U.S. Pat. No. 2,954,486 Potter 3,510,735 Goyer 3,629,692 Frederiksen 3,659,121 Davis 3,721,893 Tsang 3,936,813 Khajezadeh et al. 4,057,894 Khajezadeh et al. 4,100,565 Timko et al. 4,123,698 ______________________________________
The Doucette et al. U.S. Pat. No. 2,954,486 describes a semiconductor resistance element termed a "field effect varistor."
The Potter U.S. Pat. No. 3,510,735 describes an integrated circuit junction transistor with an integral base pinch resistor.
The Goyer U.S. Pat. No. 3,629,692 shows electrical circuits which provide a relatively constant predetermined current from a source of potential which may vary over a wide range of values. The circuit utilizes bipolar transistors and resistors.
The Frederiksen U.S. Pat. No. 3,659,121 shows a constant current source utilizing transistors and resistors. The Frederiksen patent states in its "Background" that attempts had been made to use a pinch resistor as the high emitter resistor in prior art constant current sources.
The David U.S. Pat. No. 3,721,893 describes a current reference circuit in which variations in the beta of the transistors of the circuit are compensated for by additional beta dependent components.
The Tsang U.S. Pat. No. 3,936,813 shows a bipolar random access memory (RAM) cell which utilizes transistors cross-coupled to form flip-flops. The flip-flop load resistors are base pinch resistors which compensate for variations in the gain (beta) of the flip-flop transistors due to normal fabrication process variations. As a result, the memory cells exhibit substantially constant read/write characteristics despite process variations.
In the Khajezadeh et al. U.S. Pat. Nos. 4,057,894 and 4,100,565, an integrated circuit includes a compensation resistor whose width varies in the same manner as the width of the base of the lateral transistor. Since the base width of the transistor has a value proportional to the beta of the transistor, the compensation resistor is connected in a circuit with the transistor to compensate for variations in the base width of the transistor.
The Timko et al. U.S. Pat. No. 4,123,698 shows an integrated circuit temperature transistor which provides a current output which is linearly related to absolute temperature. The output current is developed by resistive means based upon the difference in base-emitter voltages of a pair of transistors having conductive areas of different sizes.